Methyl-substituted biphenyl compounds, their production and their use in the manufacture of plasticizers

ABSTRACT

In a process for producing methyl-substituted biphenyl compounds, a feed comprising at least one aromatic hydrocarbon selected from the group consisting of toluene, xylene and mixtures thereof is contacted with hydrogen in the presence of a hydroalkylation catalyst under conditions effective to produce a hydroalkylation reaction product comprising (methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes. At least part of the hydroalkylation reaction product is then dehydrogenated in the presence of a dehydrogenation catalyst under conditions effective to produce a dehydrogenation reaction product comprising a mixture of methyl-substituted biphenyl compounds.

PRIORITY

This application claims the benefit of and priority to ProvisionalApplication No. 61/781,129, filed Mar. 14, 2013.

FIELD

The disclosure relates to methyl-substituted biphenyl compounds, theirproduction and their use in the manufacture of plasticizers.

BACKGROUND

Plasticizers are incorporated into a resin (usually a plastic orelastomer) to increase the flexibility, workability, or distensibilityof the resin. The largest use of plasticizers is in the production of“plasticized” or flexible polyvinyl chloride (PVC) products. Typicaluses of plasticized PVC include films, sheets, tubing, coated fabrics,wire and cable insulation and jacketing, toys, flooring materials suchas vinyl sheet flooring or vinyl floor tiles, adhesives, sealants, inks,and medical products such as blood bags and tubing, and the like.

Other polymer systems that use small amounts of plasticizers includepolyvinyl butyral, acrylic polymers, nylon, polyolefins, polyurethanes,and certain fluoroplastics. Plasticizers can also be used with rubber(although often these materials fall under the definition of extendersfor rubber rather than plasticizers). A listing of the majorplasticizers and their compatibilities with different polymer systems isprovided in “Plasticizers,” A. D. Godwin, in Applied Polymer Science21st Century, edited by C. D. Craver and C. E. Carraher, Elsevier(2000); pp. 157-175.

The most important chemical class of plasticizers is phthalic acidesters, which accounted for about 84% worldwide of PVC plasticizer usagein 2009.

Others are esters based on cyclohexanoic acid. In the late 1990's andearly 2000's, various compositions based on cyclohexanoate,cyclohexanedioates, and cyclohexanepolyoate esters were said to beuseful for a range of goods from semi-rigid to highly flexiblematerials. See, for instance, WO 99,32427, WO 2004/046078, WO2003/029339, U.S. Patent Publication No. 2006-0247461, and U.S. Pat. No.7,297,738.

Others also include esters based on benzoic acid (see, for instance,U.S. Pat. No. 6,740,254) and polyketones, such as described in U.S. Pat.No. 6,777,514; and U.S. Patent Publication No. 2008-0242895. Epoxidizedsoybean oil, which has much longer alkyl groups (C₁₆ to C₁₈), has beentried as a plasticizer, but is generally used as a PVC stabilizer.Stabilizers are used in much lower concentrations than plasticizers. USPatent Publication No. 2010-0159177 discloses triglycerides with a totalcarbon number of the triester groups between 20 and 25, produced byesterification of glycerol with a combination of acids derived from thehydroformylation and subsequent oxidation of C₃ to C₉ olefins, havingexcellent compatibility with a wide variety of resins and that can bemade with a high throughput.

For example, in an article entitled “Esters of diphenic acid and theirplasticizing properties”, Kulev et al., Izvestiya TomskogoPolitekhnicheskogo Instituta (1961) 111, disclose that diisoamyldiphenate, bis(2-ethylhexyl)diphenate and mixed heptyl, octyl and nonyldiphenates can be prepared by esterification of diphenic acid, andallege that the resultant esters are useful as plasticizers for vinylchloride. Similarly, in an article entitled “Synthesis of dialkyldiphenates and their properties”, Shioda et al., Yuki Gosei KagakuKyokaishi (1959), 17, disclose that dialkyl diphenates of C₁ to C₈alcohols, said to be useful as plasticizers for poly(vinyl chloride),can be formed by converting diphenic acid to diphenic anhydride andesterifying the diphenic anhydride. However, since these processesinvolve esterification of diphenic acid or anhydride, they necessarilyresult in 2,2′-substituted diesters of diphenic acid. Generally, suchdiesters having substitution on the 2-carbons have proven to be toovolatile for use as plasticizers.

An alternative method of producing dialkyl diphenate esters having anincreased proportion of the less volatile 3,3′, 3,4′ and 4,4′ diestershas now been developed. In particular, it has been found thatdimethylbiphenyl compounds containing significant amounts of the3,3′-dimethyl, the 3,4′-dimethyl and the 4,4′-dimethyl isomers can beeconomically produced by hydroalkylation of toluene and/or xylenefollowed by dehydrogenation of the resulting (methylcyclohexyl)tolueneand/or (dimethylcyclohexyl)xylene product. The resultant mixture can beused as a precursor in the production of biphenylester-basedplasticizers by, for example, oxidizing the methyl-substituted biphenylcompounds to convert at least one of the methyl groups to a carboxylicacid group and then esterifying the carboxylic acid group with analcohol, such as an oxo alcohol. In addition, depending on the catalystemployed, the hydroalkylation reaction exhibits low selectivity to fullysaturated compounds, which are difficult to dehydrogenate to biphenyls,and low selectivity to heavies, which must be removed resulting in yieldloss.

SUMMARY

In one aspect, the present disclosure is directed to a process forproducing methyl-substituted biphenyl compounds, the process comprising:

(a) contacting a feed comprising at least one aromatic hydrocarbonselected from the group consisting of toluene, xylene and mixturesthereof with hydrogen in the presence of a hydroalkylation catalystunder conditions effective to produce a hydroalkylation reaction productcomprising (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes; and

(b) dehydrogenating at least part of the hydroalkylation reactionproduct in the presence of a dehydrogenation catalyst under conditionseffective to produce a dehydrogenation reaction product comprising amixture of methyl-substituted biphenyl compounds.

In another aspect, the present disclosure is directed to a process forproducing biphenyl esters, the process comprising:

(a) contacting a feed comprising at least one aromatic hydrocarbonselected from the group consisting of toluene, xylene and mixturesthereof with hydrogen in the presence of a hydroalkylation catalystunder conditions effective to produce a hydroalkylation reaction productcomprising (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes;

(b) dehydrogenating at least part of the hydroalkylation reactionproduct in the presence of a dehydrogenation catalyst under conditionseffective to produce a dehydrogenation reaction product comprising amixture of methyl-substituted biphenyl compounds;

(c) contacting at least part of the dehydrogenation reaction productwith an oxidizing gas under conditions effective to convert at leastpart of the methyl-substituted biphenyl compounds to biphenyl carboxylicacids; and

(d) reacting the biphenyl carboxylic acids with one or more C₄ to C₁₄alcohols under conditions effective to produce biphenyl esters.

In one embodiment, the hydroalkylation catalyst comprises an acidiccomponent and a hydrogenation component. The acidic component maycomprise a molecular sieve, such as a molecular sieve selected from thegroup consisting of BEA, FAU and MTW structure type molecular sieves,molecular sieves of the MCM-22 family and mixtures thereof. In oneembodiment, the acidic component comprises a molecular sieve of theMCM-22 family.

In yet another aspect, the present disclosure is directed to a processfor producing (methylcyclohexyl)toluene, the process comprising:

(a) contacting a feed comprising toluene with hydrogen in the presenceof a hydroalkylation catalyst under conditions effective to produce ahydroalkylation reaction product comprising (methylcyclohexyl)toluene,wherein the hydroalkylation catalyst comprises a molecular sieve of theMCM-22 family and a hydrogenation metal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bar graph comparing the amount ofdi(methylcyclohexyl)toluenes produced in the hydroalkylation of tolueneover the catalysts of Examples 1 to 4.

FIG. 2 is a graph of toluene conversion against time on stream (TOS) inthe hydroalkylation of toluene over the Pd-MCM-49 catalyst of Example 1.

FIG. 3 is a graph of toluene conversion against time on stream (TOS) inthe hydroalkylation of toluene over the Pd-beta catalyst of Example 2.

FIG. 4 is a graph of toluene conversion against time on stream (TOS) inthe hydroalkylation of toluene over the Pd—Y catalyst of Example 3.

FIG. 5 is a graph of toluene conversion against time on stream (TOS) inthe hydroalkylation of toluene over the Pd—WO₃/ZrO₂ catalyst of Example4.

FIG. 6 is a bar graph comparing the reaction effluents produced by thenon-selective dehydrogenation of the hydroalkylation products ofExamples 1 and 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure relates to the production of methyl substitutedbiphenyl compounds by the catalytic hydroalkylation of toluene and/orxylene followed by dehydrogenation of at least part of thehydroalkylation reaction product. Depending on the catalyst employed inthe hydroalkylation reaction, the hydroalkylation process is selectiveto the production of the desired (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes without excessive production of heavies andfully saturated rings. In addition, the dimethylbiphenyl product of thedehydrogenation reaction contains significant amounts of the3,3′-dimethyl, the 3,4′-dimethyl and the 4,4′-dimethyl compounds makingthe product an attractive precursor in the production ofbiphenylester-based plasticizers.

Hydroalkylation of Toluene and/or Xylene

Hydroalkylation is a two-stage catalytic reaction in which an aromaticcompound is partially hydrogenated to produce a cyclic olefin, whichthen reacts, in situ, with the aromatic compound to produce acycloalkylaromatic product. In the present process, the aromaticcompound comprises toluene and/or xylene and the cycloalkylaromaticproduct comprises a mixture of (methylcyclohexyl)toluene and/or(dimethylcyclohexyl)xylene isomers. In the case of toluene, the desiredreaction may be summarized as follows:

Among the competing reactions is further hydrogenation of the cyclicolefin intermediate and/or the cycloalkylaromatic product to producefully saturated rings. In the case of toluene as the hydroalkylationfeed, further hydrogenation can produce methylcyclohexane anddimethylbicyclohexane compounds. Although these by-products can beconverted back to feed (toluene) and to the product((methylcyclohexyl)toluene and dimethylbiphenyl) via dehydrogenation,this involves an endothermic reaction requiring high temperatures (>375°C.) to obtain high conversion. This not only makes the reaction costlybut can also lead to further by-product formation and hence yield loss.It is therefore desirable to employ a hydroalkylation catalyst thatexhibits low selectivity towards the production of fully saturatedrings.

Another competing reaction is dialkylation in which the(methylcyclohexyl)toluene product reacts with further methylcyclohexeneto produce di(methylcyclohexyl)toluene. Again this by-product can beconverted back to (methylcyclohexyl)toluene, in this case bytransalkylation. However, this process requires the use of an acidcatalyst at temperatures above 160° C. and can lead to the production ofadditional by-products, such as di(methylcyclopentyl)toluenes,cyclohexylxylenes and cyclohexylbenzene. It is therefore desirable toemploy a hydroalkylation catalyst that exhibits low selectivity towardsdi(methylcyclohexyl)toluene and other heavy by-products.

The catalyst employed in the hydroalkylation reaction is a bifunctionalcatalyst comprising a hydrogenation component and a solid acidalkylation component, typically a molecular sieve. The catalyst may alsoinclude a binder such as clay, silica and/or metal oxides. The lattermay be either naturally occurring or in the form of gelatinousprecipitates or gels including mixtures of silica and metal oxides.Naturally occurring clays which can be used as a binder include those ofthe montmorillonite and kaolin families, which families include thesubbentonites and the kaolins commonly known as Dixie, McNamee, Ga. andFlorida clays or others in which the main mineral constituent ishalloysite, kaolinite, dickite, nacrite or anauxite. Such clays can beused in the raw state as originally mined or initially subjected tocalcination, acid treatment or chemical modification. Suitable metaloxide binders include silica, alumina, zirconia, titania,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia.

Any known hydrogenation metal or compound thereof can be employed as thehydrogenation component of the catalyst, although suitable metalsinclude palladium, ruthenium, nickel, zinc, tin, and cobalt, withpalladium being particularly advantageous. In certain embodiments, theamount of hydrogenation metal present in the catalyst is between about0.05 and about 10 wt %, such as between about 0.1 and about 5 wt %, ofthe catalyst.

In one embodiment, the solid acid alkylation component comprises a largepore molecular sieve having a Constraint Index (as defined in U.S. Pat.No. 4,016,218) less than 2. Suitable large pore molecular sieves includezeolite beta, zeolite Y, Ultrastable Y (USY), Dealuminized Y (Deal Y),mordenite, ZSM-3, ZSM-4, ZSM-18, and ZSM-20. Zeolite ZSM-14 is describedin U.S. Pat. No. 3,923,636. Zeolite ZSM-20 is described in U.S. Pat. No.3,972,983. Zeolite Beta is described in U.S. Pat. No. 3,308,069, and Re.No. 28,341. Low sodium Ultrastable Y molecular sieve (USY) is describedin U.S. Pat. Nos. 3,293,192 and 3,449,070. Dealuminized Y zeolite (DealY) may be prepared by the method found in U.S. Pat. No. 3,442,795.Zeolite UHP-Y is described in U.S. Pat. No. 4,401,556. Mordenite is anaturally occurring material but is also available in synthetic forms,such as TEA-mordenite (i.e., synthetic mordenite prepared from areaction mixture comprising a tetraethylammonium directing agent).TEA-mordenite is disclosed in U.S. Pat. Nos. 3,766,093 and 3,894,104.

In another, more preferred embodiment, the solid acid alkylationcomponent comprises a molecular sieve of the MCM-22 family. The term“MCM-22 family material” (or “material of the MCM-22 family” or“molecular sieve of the MCM-22 family”), as used herein, includes one ormore of:

-   -   molecular sieves made from a common first degree crystalline        building block unit cell, which unit cell has the MWW framework        topology. (A unit cell is a spatial arrangement of atoms which        if tiled in three-dimensional space describes the crystal        structure. Such crystal structures are discussed in the “Atlas        of Zeolite Framework Types”, Fifth edition, 2001, the entire        content of which is incorporated as reference);    -   molecular sieves made from a common second degree building        block, being a 2-dimensional tiling of such MWW framework        topology unit cells, forming a monolayer of one unit cell        thickness, preferably one c-unit cell thickness;    -   molecular sieves made from common second degree building blocks,        being layers of one or more than one unit cell thickness,        wherein the layer of more than one unit cell thickness is made        from stacking, packing, or binding at least two monolayers of        one unit cell thickness. The stacking of such second degree        building blocks can be in a regular fashion, an irregular        fashion, a random fashion, or any combination thereof; and    -   molecular sieves made by any regular or random 2-dimensional or        3-dimensional combination of unit cells having the MWW framework        topology.

Molecular sieves of MCM-22 family generally have an X-ray diffractionpattern including d-spacing maxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and3.42±0.07 Angstrom. The X-ray diffraction data used to characterize thematerial are obtained by standard techniques using the K-alpha doubletof copper as the incident radiation and a diffractometer equipped with ascintillation counter and associated computer as the collection system.Molecular sieves of MCM-22 family include MCM-22 (described in U.S. Pat.No. 4,954,325), PSH-3 (described in U.S. Pat. No. 4,439,409), SSZ-25(described in U.S. Pat. No. 4,826,667), ERB-1 (described in EuropeanPatent No. 0293032), ITQ-1 (described in U.S. Pat. No. 6,077,498), ITQ-2(described in International Patent Publication No. WO97/17290), MCM-36(described in U.S. Pat. No. 5,250,277), MCM-49 (described in U.S. Pat.No. 5,236,575), MCM-56 (described in U.S. Pat. No. 5,362,697) andmixtures thereof.

In addition to the toluene and/or xylene and hydrogen, a diluent, whichis substantially inert under hydroalkylation conditions, may be includedin the feed to the hydroalkylation reaction. In certain embodiments, thediluent is a hydrocarbon, in which the desired cycloalkylaromaticproduct is soluble, such as a straight chain paraffinic hydrocarbon, abranched chain paraffinic hydrocarbon, and/or a cyclic paraffinichydrocarbon. Examples of suitable diluents are decane and cyclohexane.Although the amount of diluent is not narrowly defined, desirably thediluent is added in an amount such that the weight ratio of the diluentto the aromatic compound is at least 1:100; for example at least 1:10,but no more than 10:1, desirably no more than 4:1.

In one embodiment, the aromatic feed to the hydroalkylation reactionalso includes benzene and/or one or more alkylbenzenes different fromtoluene and xylene. Suitable alkylbenzenes may have one or more alkylgroups with up to 4 carbon atoms and include, by way of example,ethylbenzene, cumene, and unseparated C₆-C₈ or C₇-C₈ or C₇-C₉ streams.

The hydroalkylation reaction can be conducted in a wide range of reactorconfigurations including fixed bed, slurry reactors, and/or catalyticdistillation towers. In addition, the hydroalkylation reaction can beconducted in a single reaction zone or in a plurality of reaction zones,in which at least the hydrogen is introduced to the reaction in stages.Suitable reaction temperatures are between about 100° C. and about 400°C., such as between about 125° C. and about 250° C., while suitablereaction pressures are between about 100 and about 7,000 kPa, such asbetween about 500 and about 5,000 kPa. The molar ratio of hydrogen toaromatic feed is typically from about 0.15:1 to about 15:1.

In the present process, it is found that MCM-22 family molecular sievesare particularly active and stable catalysts for the hydroalkylation oftoluene or xylene. In addition, catalysts containing MCM-22 familymolecular sieves exhibit improved selectivity to the 3,3′-dimethyl, the3,4′-dimethyl, the 4,3′-dimethyl and the 4,4′-dimethyl isomers in thehydroalkylation product, while at the same time reducing the formationof fully saturated and heavy by-products. For example, using an MCM-22family molecular sieve with a toluene feed, it is found that thehydroalkylation reaction product may comprise:

-   -   at least 60 wt %, such as at least 70 wt %, for example at least        80 wt % of the 3,3,3,4,4,3 and 4,4-isomers of        (methylcyclohexyl)toluene based on the total weight of all the        (methylcyclohexyl)toluene isomers;    -   less than 30 wt % of methylcyclohexane and less than 2% of        dimethylbicyclohexane compounds; and    -   less than 1 wt % of compounds containing in excess of 14 carbon        atoms.

Similarly, with a xylene feed, the hydroalkylation reaction product maycomprise less than 1 wt % of compounds containing in excess of 16 carbonatoms.

By way of illustration, the 3,3, 3,4 4,3 and 4,4-isomers of(methylcyclohexyl)toluene are illustrated in formulas F1 to F4,respectively:

In contrast, when the methyl group is located in the 1-position(quaternary carbon) on the cyclohexyl ring, ring isomerization can occurforming (dimethylcyclopentyl)toluene and (ethylcyclopentyl)toluenewhich, on dehydrogenation, will generate diene by-products which aredifficult to separate from the desired product and will also inhibit thesubsequent oxidation reaction. In the oxidation and esterificationsteps, different isomers have different reactivity. Thus, para-isomersare more reactive than meta-isomers which are more reactive thanortho-isomers. Also in the dehydrogenation step, the presence of amethyl group in the 2 position on either the cyclohexyl or phenyl ringis a precursor for the formation of fluorene and methyl fluorene.Fluorene is difficult to separate from the dimethylbiphenyl product andcauses problems in the oxidation step and also in the plasticizersperformance. It is therefore advantageous to minimize the formation ofisomers which have a methyl group in the ortho, 2 and benzylicpositions.

Dehydrogenation of Hydroalkylation Product

The major components of the hydroalkylation reaction effluent are(methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes, unreactedaromatic feed (toluene and/or xylene) and fully saturated single ringby-products (methylcyclohexane and dimethylcyclohexane). The unreactedfeed and light by-products can readily be removed from the reactioneffluent by, for example, distillation. The unreacted feed can then berecycled to the hydroalkylation reactor, while the saturated by-productscan be dehydrogenated to produce additional recyclable feed.

The remainder of the hydroalkylation reaction effluent, composed mainlyof (methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes, isthen dehydrogenated to produce the corresponding methyl-substitutedbiphenyl compounds. The dehydrogenation is conveniently conducted at atemperature from about 200° C. to about 600° C. and a pressure fromabout 100 kPa to about 3550 kPa (atmospheric to about 500 psig) in thepresence of dehydrogenation catalyst. A suitable dehydrogenationcatalyst comprises one or more elements or compounds thereof selectedfrom Group 10 of the Periodic Table of Elements, for example platinum,on a support, such as silica, alumina or carbon nanotubes. In oneembodiment, the Group 10 element is present in amount from 0.1 to 5 wt %of the catalyst. In some cases, the dehydrogenation catalyst may alsoinclude tin or a tin compound to improve the selectivity to the desiredmethyl-substituted biphenyl product. In one embodiment, the tin ispresent in amount from 0.05 to 2.5 wt % of the catalyst.

As used herein, the numbering scheme for the Periodic Table Groups is asdisclosed in Chemical and Engineering News, 63(5), 27 (1985).

Particularly using an MCM-22 family-based catalyst for the upstreamhydroalkylation reaction, the product of the dehydrogenation stepcomprises methyl-substituted biphenyl compounds in which theconcentration of the 3,3-, 3,4- and 4,4-dimethyl isomers is at least 50wt %, such as at least 60 wt %, for example at least 70 wt % based onthe total weight of methyl-substituted biphenyl isomers. In addition,the product may contain less than 10 wt %, such as less than 5 wt %, forexample less than 3 wt % of methyl biphenyl compounds and less than 5 wt%, such as less than 3 wt %, for example less than 1 wt % of fluoreneand methyl fluorenes combined.

Production of Biphenyl Esters

The methyl-substituted biphenyl compounds produced by thedehydrogenation reaction can readily be converted ester plasticizers bya process comprising oxidation to produce the corresponding carboxylicacids followed by esterification with an alcohol.

The oxidation can be performed by any process known in the art, such asby reacting the methyl-substituted biphenyl compounds with an oxidant,such as oxygen, ozone or air, or any other oxygen source, such ashydrogen peroxide, in the presence of a catalyst at temperatures from30° C. to 300° C., such as from 60° C. to 200° C. Suitable catalystscomprise Co or Mn or a combination of both metals.

The resulting carboxylic acids can then be esterified to producebiphenyl ester plasticizers by reaction with one or more C₄ to C₁₄alcohols. Suitable esterification conditions are well-known in the artand include, but are not limited to, temperatures of 0-300° C. and thepresence or absence of homogeneous or heterogeneous esterificationcatalysts, such as Lewis or Bronsted acid catalysts. Suitable alcoholsare “oxo-alcohols”, by which is meant an organic alcohol, or mixture oforganic alcohols, which is prepared by hydroformylating an olefin,followed by hydrogenation to form the alcohols. Typically, the olefin isformed by light olefin oligomerization over heterogeneous acidcatalysts, which olefins are readily available from refinery processingoperations. The reaction results in mixtures of longer-chain, branchedolefins, which subsequently form longer chain, branched alcohols, asdescribed in U.S. Pat. No. 6,274,756, incorporated herein by referencein its entirety. Another source of olefins used in the OXO process arethrough the oligomerization of ethylene, producing mixtures ofpredominately straight chain alcohols with lesser amounts of lightlybranched alcohols.

The biphenyl ester plasticizers of the present application find use in anumber of different polymers, such as vinyl chloride resins, polyesters,polyurethanes, ethylene-vinyl acetate copolymers, rubbers,poly(meth)acrylics and mixtures thereof.

The invention will now be more particularly described with reference tothe accompanying drawings and the following non-limiting Examples.

Example 1: Synthesis of 0.3% Pd/MCM-49 Catalyst

80 parts MCM-49 zeolite crystals are combined with 20 partspseudoboehmite alumina, on a calcined dry weight basis. The MCM-49 andpseudoboehmite alumina dry powder is placed in a muller and mixed forabout 10 to 30 minutes. Sufficient water and 0.05% polyvinyl alcohol isadded to the MCM-49 and alumina during the mixing process to produce anextrudable paste. The extrudable paste is formed into a 1/20 inch (0.13cm) quadrulobe extrudate using an extruder and the resulting extrudateis dried at a temperature ranging from 250° F. to 325° F. (120° C. to163° C.). After drying, the dried extrudate is heated to 1000° F. (538°C.) under flowing nitrogen. The extrudate is then cooled to ambienttemperature and humidified with saturated air or steam.

After the humidification, the extrudate is ion exchanged with 0.5 to 1 Nammonium nitrate solution. The ammonium nitrate solution ion exchange isrepeated. The ammonium nitrate exchanged extrudate is then washed withdeionized water to remove residual nitrate prior to calcination in air.After washing the wet extrudate, it is dried. The exchanged and driedextrudate is then calcined in a nitrogen/air mixture to a temperature1000° F. (538° C.). Afterwards, the calcined extrudate is cooled to roomtemperature. The 80% MCM-49, 20% Al₂O₃ extrudate was incipient wetnessimpregnated with a palladium (II) chloride solution (target: 0.30% Pd)and then dried overnight at 121° C. The dried catalyst was calcined inair at the following conditions: 5 volumes air per volume catalyst perminute, ramp from ambient to 538° C. at 1° C./min and hold for 3 hours.

Example 2: Synthesis of 0.3% Pd/Beta Catalyst

80 parts beta zeolite crystals are combined with 20 parts pseudoboehmitealumina, on a calcined dry weight basis. The beta and pseudoboehmite aremixed in a muller for about 15 to 60 minutes. Sufficient water and 1.0%nitric acid is added during the mixing process to produce an extrudablepaste. The extrudable paste is formed into a 1/20 inch quadrulobeextrudate using an extruder. After extrusion, the 1/20th inch quadrulobeextrudate is dried at a temperature ranging from 250° F. to 325° F.(120° C. to 163° C.). After drying, the dried extrudate is heated to1000° F. (538° C.) under flowing nitrogen and then calcined in air at atemperature of 1000° F. (538° C.). Afterwards, the calcined extrudate iscooled to room temperature. The 80% Beta, 20% Al₂O₃ extrudate wasincipient wetness impregnated with a tetraammine palladium (II) nitratesolution (target: 0.30% Pd) and then dried overnight at 121° C. Thedried catalyst was calcined in air at the following conditions: 5volumes air per volume catalyst per minute, ramp from ambient to 538° C.at 1° C./min and hold for 3 hours.

Example 3: Synthesis of 0.3% Pd/USY Catalyst

80 parts Zeolyst CBV-720 ultrastable Y zeolite crystals are combinedwith 20 parts pseudoboehmite alumina on a calcined dry weight basis. TheUSY and pseudoboehmite are mixed for about 15 to 60 minutes. Sufficientwater and 1.0% nitric acid is added during the mixing process to producean extrudable paste. The extrudable paste is formed into a 1/20 inchquadrulobe extrudate using an extruder. After extrusion, the 1/20th inchquadrulobe extrudate is dried at a temperature ranging from 250° F. to325° F. (120° C. to 163° C.). After drying, the dried extrudate isheated to 1000° F. (538° C.) under flowing nitrogen and then calcined inair at a temperature of 1000° F. (538° C.). The 80% CBV-720 USY, 20%Al₂O₃ extrudate was incipient wetness impregnated with a palladium (II)chloride solution (target: 0.30% Pd) and then dried overnight at 121° C.The dried catalyst was calcined in air at the following conditions: 5volumes air per volume catalyst per minute, ramp from ambient to 538° C.at 1° C./min and hold for 3 hours.

Example 4: Synthesis of 0.3% Pd/W—Zr Catalyst

A WO₃/ZrO₂ extrudate (11.5% W, balance Zr) 1/16″ cylinder was obtainedfrom Magnesium Elektron in the form of a 1/16 inch (0.16 cm) diameterextrudate. The WO₃/ZrO₂ extrudate was calcined in air for 3 hours at538° C. On cooling, the calcined extrudate was incipient wetnessimpregnated with a palladium (II) chloride solution (target: 0.30% Pd)and then dried overnight at 121° C. The dried catalyst was calcined inair at the following conditions: 5 volumes air per volume catalyst perminute, ramp from ambient to 538° C. at 1° C./min and hold for 3 hours.

Example 5: Hydroalkylation Catalyst Testing

Each of the catalyst of Examples 1 to 4 was then tested in thehydroalkylation of a toluene feed using the reactor and processdescribed below.

The reactor comprised a stainless steel tube having an outside diameterof: ⅜ inch (0.95 cm), a length of 20.5 inch (52 cm) and a wall thicknessof 0.35 inch (0.9 cm). A piece of stainless steel tubing having a lengthof 8¾ inch (22 cm) and an outside diameter of: ⅜ inch (0.95 cm) and asimilar length of ¼ inch (0.6 cm) tubing of were used in the bottom ofthe reactor (one inside of the other) as a spacer to position andsupport the catalyst in the isothermal zone of the furnace. A ¼ inch(0.6 cm) plug of glass wool was placed on top of the spacer to keep thecatalyst in place. A ⅛ inch (0.3 cm) stainless steel thermo-well wasplaced in the catalyst bed to monitor temperature throughout thecatalyst bed using a movable thermocouple.

The catalyst was sized to 20/40 sieve mesh or cut to 1:1 length todiameter ratio, dispersed with quartz chips (20/40 mesh) then loadedinto the reactor from the top to a volume of 5.5 cc. The catalyst bedtypically was 15 cm. in length. The remaining void space at the top ofthe reactor was filled with quartz chips, with a ¼ plug of glass woolplaced on top of the catalyst bed being used to separate quartz chipsfrom the catalyst. The reactor was installed in a furnace with thecatalyst bed in the middle of the furnace at a pre-marked isothermalzone. The reactor was then pressure and leak tested typically at 300psig (2170 kPa).

The catalyst was pre-conditioned in situ by heating to 25° C. to 240° C.with H₂ flow at 100 cc/min and holding for 12 hours. A 500 cc ISCOsyringe pump was used to introduce a chemical grade toluene feed to thereactor. The feed was pumped through a vaporizer before flowing throughheated lines to the reactor. A Brooks mass flow controller was used toset the hydrogen flow rate. A Grove “Mity Mite” back pressure controllerwas used to control the reactor pressure typically at 150 psig (1135kPa). GC analyses were taken to verify feed composition. The feed wasthen pumped through the catalyst bed held at the reaction temperature of120° C. to 180° C. at a WHSV of 2 and a pressure of 15-200 psig(204-1480 kPa). The liquid products exiting the reactor flowed throughheated lines routed to two collection pots in series, the first potbeing heated to 60° C. and the second pot cooled with chilled coolant toabout 10° C. Material balances were taken at 12 to 24 hrs intervals.Samples were taken and diluted with 50% ethanol for analysis. An Agilent7890 gas chromatograph with FID detector was used for the analysis. Thenon-condensable gas products were routed to an on line HP 5890 GC.

The analysis is done on an Agilent 7890 GC with 150 vial sample tray.

Inlet Temp: 220° C.

Detector Temp: 240° C. (Col+make up=constant)

Temp Program Initial temp 120° C. hold for 15 min., ramp at 2° C./min to180° C., hold 15 min; ramp at 3° C./min. to 220° C. and hold till end.

Column Flow: 2.25 ml/min. (27 cm/sec); Split mode, Split ratio 100:1

Injector: Auto sampler (0.2 n1).

Column Parameters:

Two columns joined to make 120 Meters (coupled with Agilent ultimateunion, deactivated.

Column # Front end: Supelco β-Dex 120; 60 m×0.25 mm×0.25 μm film joinedto

Column #2 back end: γ-Dex 325: 60 m×0.25 mm×0.25 μm film.

The results of the hydroalkylation testing are summarized in FIGS. 1 to4 and Table 1.

TABLE 1 Toluene Selectivity Selectivity conver- to methyl- todimethylbi- Example Catalyst sion cyclohexane (cyclohexane) 1 0.3%Pd-MCM49 37% 23% 1.40% 2 0.3% Pd/Beta 40% 65% 1.60% 3 0.3% Pd/Y 80% 75%3.70% 4 0.3% WO3/ZrO2 13% 35% 1.75%

As can be seen from Table 1, although the Pd/MCM-49 catalyst is lessactive than the Pd/Y catalyst, it has much lower selectivity towards theproduction of the fully saturated by-products, methylcyclohexane anddimethylbi(cyclohexane) than either Pd/Y or Pd/beta. In addition, thedata shown in FIG. 1 clearly demonstrate that Pd/MCM-49 provides thelowest yield loss, less than 1 wt % of total converted feed, todialkylate products. The data shown in FIGS. 2 to 5 demonstrate thatPd/MCM-49 has improved stability and catalyst life as compared with theother catalysts tested. It is believed that the stability is related tothe formation of heavies which remain on the surface of the catalyst andreact further to create coke which prevents the access to the acid andhydrogenation sites.

Example 6: Dehydrogenation of Methylcyclohexyltoluene

The same reactor, catalyst and analytical configuration as describedabove was used to perform dehydrogenation tests on the conversionproducts produced in Example 5 from the Pd/MCM-49 and Pd/beta catalystsof Examples 1 and 2, except each dehydrogenation catalyst waspre-conditioned in situ by heating to 375° C. to 460° C. with H₂ flow at100 cc/min and holding for 2 hours. In addition, in the dehydrogenationtests the catalyst bed was held at the reaction temperature of 375° C.to 460° C. at a WHSV of 2 and a pressure of 100 psig (790 kPa).

In a first set of tests, the dehydrogenation was conducted at atemperature of 425° C. using a selective dehydrogenation catalystcomprising bimetallic catalyst e.g., Pt/Sn, on a support. The results ofthe tests are summarized in Table 2 below:

TABLE 2 MCM-49 HA product Beta HA product over selective over selectivedehydrogenation dehydrogenation catalyst catalyst 3-methyl biphenyl0.70% 2.47% 4-methyl biphenyl 0.79% 4.98% 2,2 dimethyl biphenyl 1.21%1.04% 2,3 dimethyl biphenyl 9.52% 8.42% 2,4 dimethyl biphenyl 13.14%12.64% 3,3 dimethyl biphenyl 15.98% 13.21% 3,4 dimethyl biphenyl 39.64%36.26% 4,4 dimethyl biphenyl 18.76% 18.19% fluorene 0.00% 0.93% methylfluorenes 0.26% 1.87%

In a second set of tests, the dehydrogenation was conducted at atemperature of 425° C. using a non-selective dehydrogenation catalystcomprising Pt on a support. The results of the tests are summarized inFIG. 6.

The data clearly shows that dehydrogenation of the MCM-49hydroalkylation products provides less mono methyl biphenyl, less of the2′,3 and 2′,4 dimethyl biphenyl isomers which are the precursor for theformation of fluorene and methyl fluorene and much less the fluorene andmethyl fluorene as compared with dehydrogenation of the zeolite betahydroalkylation products.

While various embodiments have been described, it is to be understoodthat further embodiments will be apparent to those skilled in the artand that such embodiments are to be considered within the purview andscope of the appended claims.

All documents described herein are incorporated by reference herein,including any priority documents and/or testing procedures to the extentthey are not inconsistent with this text, provided however that anypriority document not named in the initially filed application or filingdocuments is NOT incorporated by reference herein. As is apparent fromthe foregoing general description and the specific embodiments, whileforms of the invention have been illustrated and described, variousmodifications can be made without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the invention belimited thereby. Likewise, the term “comprising” is consideredsynonymous with the term “including” for purposes of Australian law.Likewise whenever a composition, an element or a group of elements ispreceded with the transitional phrase “comprising”, it is understoodthat we also contemplate the same composition or group of elements withtransitional phrases “consisting essentially of,” “consisting of”,“selected from the group of consisting of,” or “is” preceding therecitation of the composition, element, or elements and vice versa.

The invention claimed is:
 1. A process for producing methyl-substitutedbiphenyl compounds, the process comprising: (a) contacting an aromaticfeed comprising toluene with hydrogen in the presence of ahydroalkylation catalyst under conditions effective to produce ahydroalkylation reaction product comprising: i)(methylcyclohexyl)toluenes; ii) at least 60 wt % of 3,3′-, 3,4′-, 4,3′-and 4,4′-isomers of (methylcyclohexyl)toluene based on the total weightof all the (methylcyclohexyl)toluene isomers; iii) less than 30 wt % ofmethylcyclohexane; and (b) dehydrogenating at least part of thehydroalkylation reaction product in the presence of a dehydrogenationcatalyst under conditions effective to produce a dehydrogenationreaction product comprising a mixture of methyl-substituted biphenylcompounds, wherein the hydroalkylation catalyst comprises an acidiccomponent and a hydrogenation component, wherein the hydrogenationcomponent comprises palladium, and where the acidic component comprisesan MCM-22 family molecular sieve.
 2. The process of claim 1, wherein theconditions in the contacting (a) include a temperature from about 100°C. to about 400° C. and a pressure from about 100 to about 7,000 kPa. 3.The process of claim 1, wherein the molar ratio of hydrogen to aromaticfeed supplied to the contacting (a) is from about 0.15:1 to about 15:1.4. The process of claim 1, wherein the hydroalkylation reaction productcomprises less than 2% of dimethylbi(cyclohexane) compounds.
 5. Theprocess of claim 1, wherein the hydroalkylation reaction productcomprises less than 1 wt % of compounds containing in excess of 14carbon atoms.
 6. The process of claim 1, wherein the feed furthercomprises benzene and/or at least one alkylbenzene different fromtoluene.
 7. The process of claim 1, wherein the dehydrogenation catalystcomprises an element or compound thereof selected from Group 10 of thePeriodic Table of Elements.
 8. The process of claim 1, wherein thedehydrogenation conditions in (b) include a temperature from about 200°C. to about 600° C. and a pressure from about 100 kPa to about 3550 kPa.9. A process for producing biphenyl esters, the process comprising: (a)contacting an aromatic feed comprising toluene with hydrogen in thepresence of a hydroalkylation catalyst under conditions effective toproduce a hydroalkylation reaction product comprising: a)(methylcyclohexyl)toluenes; b) at least 60 wt % of 3,3′-, 3,4′-, 4,3′-and 4,4′-isomers of (methylcyclohexyl)toluene based on the total weightof all the (methylcyclohexyl)toluene isomers; c) less than 30 wt % ofmethylcyclohexane; and (b) dehydrogenating at least part of thehydroalkylation reaction product in the presence of a dehydrogenationcatalyst under conditions effective to produce a dehydrogenationreaction product comprising a mixture of methyl-substituted biphenylcompounds, wherein the hydroalkylation catalyst comprises an acidiccomponent and a hydrogenation component, wherein the hydrogenationcomponent comprises palladium, and where the acidic component comprisesan MCM-22 family molecular sieve; (c) contacting at least part of thedehydrogenation reaction product with an oxidant under conditionseffective to convert at least part of the methyl-substituted biphenylcompounds to biphenyl carboxylic acids; and (d) reacting the biphenylcarboxylic acids with one or more C₄ to C₁₄ alcohols under conditionseffective to produce biphenyl esters.
 10. The process of claim 9,wherein the conditions in (a) include a temperature from about 100° C.to about 400° C. and a pressure from about 100 to about 7,000 kPa. 11.The process of claim 9, wherein the molar ratio of hydrogen to aromaticfeed supplied to the hydroalkylating step (a) is from about 0.15:1 toabout 15:1.
 12. The process of claim 9, wherein the dehydrogenationcatalyst comprises an element or compound thereof selected from Group 10of the Periodic Table of Elements.
 13. The process of claim 9, whereinthe dehydrogenation conditions in (b) include a temperature from about200° C. to about 600° C. and a pressure from about 100 kPa to about 3550kPa.
 14. A process for producing (methylcyclohexyl)toluene, the processcomprising: (a) contacting a feed comprising toluene with hydrogen inthe presence of a hydroalkylation catalyst under conditions effective toproduce a hydroalkylation reaction product comprising(methylcyclohexyl)toluene, wherein the hydroalkylation catalystcomprises a molecular sieve of the MCM-22 family and a hydrogenationmetal, wherein the hydrogenation metal is wherein the hydroalkylationreaction product comprises: at least 60 wt % of 3,3′-, 3,4′-, 4,3′- and4,4′-isomers of (methylcyclohexyl)toluene based on the total weight ofall the (methylcyclohexyl)toluene isomers and less than 30 wt % ofmethylcyclohexane.
 15. The process of claim 1, wherein unreactedaromatic feed is removed from the hydroalkylation reaction product ofstep a) and recycled back to the hydroalkylation of step a).
 16. Theprocess of claim 1, wherein toluene feed is removed from thehydroalkylation reaction product of step a) and recycled back to thehydroalkylation of step a).
 17. The process of claim 1 wherein fullysaturated single ring by-products in the hydroalkylation reactionproduct of step a) are dehydrogenated to produce recyclable feed that isrecycled back to the hydroalkylation of step a).
 18. The process ofclaim 1 wherein methylcyclohexane in the hydroalkylation reactionproduct of step a) are dehydrogenated to produce recyclable feed that isrecycled back to the hydroalkylation of step a).
 19. The process ofclaim 1, wherein unreacted aromatic feed is removed from thehydroalkylation reaction product of step a) and recycled back to thehydroalkylation of step a), and wherein fully saturated single ringby-products in the hydroalkylation reaction product of step a) aredehydrogenated to produce recyclable feed that is recycled back to thehydroalkylation of step a).
 20. The process of claim 1, wherein toluenefeed is removed from the hydroalkylation reaction product of step a) andrecycled back to the hydroalkylation of step a), and whereinmethylcyclohexane in the hydroalkylation reaction product of step a) aredehydrogenated to produce recyclable feed that is recycled back to thehydroalkylation of step a).
 21. The process of claim 9, whereinunreacted aromatic feed is removed from the hydroalkylation reactionproduct of step a) and recycled back to the hydroalkylation of step a),and wherein fully saturated single ring by-products in thehydroalkylation reaction product of step a) are dehydrogenated toproduce recyclable feed that is recycled back to the hydroalkylation ofstep a).
 22. The process of claim 9, wherein toluene feed is removedfrom the hydroalkylation reaction product of step a) and recycled backto the hydroalkylation of step a), and wherein methylcyclohexane in thehydroalkylation reaction product of step a) are dehydrogenated toproduce recyclable feed that is recycled back to the hydroalkylation ofstep a).
 23. The process of claim 1, wherein the dehydrogenationcatalyst comprises one or more elements selected from Group 10 and tinor a tin compound.
 24. The process of claim 1, wherein thedehydrogenation catalyst comprises platinum and tin or a tin compound.25. The process of claim 23, wherein the Group 10 element is present at0.1 to 5 wt % of the catalyst and the tin is present at from 0.05 to 2.5wt % of the catalyst.
 26. The process of claim 9, wherein thedehydrogenation catalyst comprises one or more elements selected fromGroup 10 and tin or a tin compound.
 27. The process of claim 9, whereinthe dehydrogenation catalyst comprises platinum and tin or a tincompound.
 28. The process of claim 27, wherein the Group 10 element ispresent at 0.1 to 5 wt % of the catalyst and the tin is present at from0.05 to 2.5 wt % of the catalyst.
 29. The process of claim 1, whereinthe dehydrogenation catalyst comprises one or more elements or compoundsthereof selected from Group 10 on a support comprising silica, aluminaor carbon nanotubes.
 30. The process of claim 9, wherein thedehydrogenation catalyst comprises one or more elements or compoundsthereof selected from Group 10 on a support comprising silica, aluminaor carbon nanotubes.
 31. The process of claim 29, wherein the supportcomprises alumina.
 32. The process of claim 30, wherein the supportcomprises alumina.
 33. The process of claim 31, wherein thedehydrogenation catalyst further comprises tin or a tin compound. 34.The process of claim 32, wherein the dehydrogenation catalyst furthercomprises tin or a tin compound.
 35. The process of claim 33, whereinthe Group 10 element is platinum.
 36. The process of claim 34, whereinthe Group 10 element is platinum.